The present invention relates generally to operations performed and equipment utilized in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides well control systems and associated methods.
Underbalanced drilling is a well drilling technique during which hydrostatic pressure of drilling fluid in a wellbore, plus any applied pressure, is less than a pore pressure in a zone of a formation being penetrated. At times, the pore pressure may be equal to or less than the combined hydrostatic and applied pressures, but in general the purpose is to prevent the drilling fluid from entering the formation, which could limit the future productivity of the formation.
During underbalanced drilling operations, various combinations of gasses, liquids and/or solids are injected into the wellbore and circulated to the surface. When the pore pressure is greater than the combined hydrostatic and applied pressures, fluid from the penetrated zones enters the wellbore and is produced to the surface along with the injected fluid. The fluid produced from the penetrated zones may include any combination of gas, water and oil.
To control the hydrostatic pressure at a penetrated zone, drilling operators typically vary the mixture of gasses, liquids, gels, foams and/or solids injected into the wellbore. To control the pressure applied to the wellbore, drilling operators typically adjust a choke at the surface to thereby regulate back pressure in the circulation of fluids through the wellbore. By controlling the hydrostatic and applied pressures, production of fluid from the penetrated zones may be controlled from the surface during drilling.
Unfortunately, these techniques do not permit an operator to anticipate a significant change in drilling conditions, such as a gas kick, so that surface controls can be adjusted accordingly. These techniques also do not permit an operator to anticipate how surface controls should be adjusted to account for changes in drilling activities, such as temporary cessation of actual drilling to connect another joint of drill pipe, etc.
Therefore, it may be seen that improvements are needed in well control systems and methods. These improvements would be of particular benefit in underbalanced drilling, as well as in other operations, such as managed pressure drilling.